This invention relates to an electrically actuated vehicle brake and more particularly to an improved electromagnet construction for such a brake.
In well known types of electrically actuated drum brakes for vehicles, the brake shoes are actuated by pivotal movement of a cammed lever that is supported on a backing plate. The lever carries an electromagnet which, when energized, drags against the rotating brake drum and affects pivotal movement of the lever to actuate the brake shoes. The magnet is mounted for limited movement relative to the lever so as to ride flat on the drum during braking.
Prior art electromagnets for actuating vehicle brakes have been made with cast, machined and stamped housings. In general, the housings are cup shaped and are provided with a center pole to define an annular opening. A solenoid winding is positioned within the annular opening and the opening is closed with a friction material. When an electric current is passed through the solenoid winding, the side of the magnetized housing and the friction material are drawn against the rotating brake drum to pivot the lever which in turn expands the brake shoes into frictional engagement with the brake drum. It has been found that stamped steel housings are ideal for the electromagnets due to the low cost of manufacture relative to cast or machined housings. However, it is necessary to attach a separate center pole to a stamped housing, as distinguished from forming the center pole integrally with the housing. In the past, it has been difficult to attach a separate center pole to a stamped steel housing without either loss of magnetic efficiency or a significant increase in cost.